The mammlian enzyme is part of the cell antioxidant defense mechanism. It initiates extracellular glutathione (GSH) breakdown, provides cells with a local cysteine supply and contributes to maintain intracelular GSH levels. The protein also has EC 3.4.19.13 (glutathione hydrolase) activity [3-4]. The enzyme consists of two chains that are created by the proteolytic cleavage of a single precursor polypeptide. The N-terminal L-threonine of the C-terminal subunit functions as the active site for both the cleavage and the hydrolysis reactions [3-4].